主子表 取子表的第一条数据 并与主表一起显示

当主表需要子表字段较少的情况下可以使用

SELECT 
a.*
,(select top 1 b.id from table1 where a.mianid=b.main order by b.id) as 字段1
,(select top 1 b.name from table1 where a.mianid=b.main order by b.id) as 字段2
from maintable  as a 

当主表需要子表字段较多的情况下可以使用

SELECT 

*
from maintable  as a 
	left join  table1  as b on a.mainid=b.mainid and b.id=(select top 1 id from  table1 as b1 where b1.mainid=a.mainid order by b1.id)
	left join  table2  as c ON c.mainid=a.mainid and c.id=(select top 1 id from  table2 as c1 where c1.mainid=a.mainid order by c1.id)
	left JOIN  ttable1 as d on c.id=d.t1id       and d.id=(select top 1 id from  ttable1 as d1 where c.id=d.t1id order by d1.id)
where a.id>''